高性能永久磁石と高密度磁気記録媒体における熱ゆらぎ磁気余効

概要

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This paper reports on the aftereffect of thermal fluctuation on the basis of experimental results for high-coercivity materials. The temperature dependences of the magnetic viscosity coefficient (S_v), activation volume (V_<act>), and coercive force (H_<cJ>) were examined for high-performance permanent magnets and high-density magnetic recording media. Samples with different H_<cJ> were prepared, and the dependences of S_v and V_<act> on H_<cJ> were studied at 300 K. The results show that S_v is constant and independent of the magnetic field. The logarithm of S_v is proportional to ln H_<cJ> for permanent magnets and fine particles. For longitudinal recording particles, the relationship H_<cJ>∝V_<act>^<-0.67> is obtained. For hexagonal ferrite magnets and particles, H_<cJ> is proportional to V_<act>^<-2>, and the value of V_<act> is inversely proportional to the anisotropy constant. The temperature variation of the coercive force (ΔH_<cJ>/ΔT) decreases with decreasing S_v for rare-earth magnets and CoCrTa/Cr thin films. Addition of Sn to Nd-Fe-B sintered magnets reduced S_v by about 1/2 at 300 K. In CoCrTa/Cr thin films, the medium noise is proportional to kT/S_v. kT/S_v and ΔH_c/ΔT increase with increasing temperature.
社団法人日本磁気学会の論文
1998-01-01